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  <div class="section" id="advice-on-packaging-llvm">
<h1>Advice on Packaging LLVM<a class="headerlink" href="#advice-on-packaging-llvm" title="Permalink to this headline">¶</a></h1>
<div class="contents local topic" id="contents">
<ul class="simple">
<li><a class="reference internal" href="#overview" id="id1">Overview</a></li>
<li><a class="reference internal" href="#compile-flags" id="id2">Compile Flags</a></li>
<li><a class="reference internal" href="#c-features" id="id3">C++ Features</a></li>
<li><a class="reference internal" href="#shared-library" id="id4">Shared Library</a></li>
<li><a class="reference internal" href="#dependencies" id="id5">Dependencies</a></li>
</ul>
</div>
<div class="section" id="overview">
<h2><a class="toc-backref" href="#id1">Overview</a><a class="headerlink" href="#overview" title="Permalink to this headline">¶</a></h2>
<p>LLVM sets certain default configure options to make sure our developers don&#8217;t
break things for constrained platforms.  These settings are not optimal for most
desktop systems, and we hope that packagers (e.g., Redhat, Debian, MacPorts,
etc.) will tweak them.  This document lists settings we suggest you tweak.</p>
<p>LLVM&#8217;s API changes with each release, so users are likely to want, for example,
both LLVM-2.6 and LLVM-2.7 installed at the same time to support apps developed
against each.</p>
</div>
<div class="section" id="compile-flags">
<h2><a class="toc-backref" href="#id2">Compile Flags</a><a class="headerlink" href="#compile-flags" title="Permalink to this headline">¶</a></h2>
<p>LLVM runs much more quickly when it&#8217;s optimized and assertions are removed.
However, such a build is currently incompatible with users who build without
defining <code class="docutils literal"><span class="pre">NDEBUG</span></code>, and the lack of assertions makes it hard to debug problems
in user code.  We recommend allowing users to install both optimized and debug
versions of LLVM in parallel.  The following configure flags are relevant:</p>
<dl class="docutils">
<dt><code class="docutils literal"><span class="pre">--disable-assertions</span></code></dt>
<dd>Builds LLVM with <code class="docutils literal"><span class="pre">NDEBUG</span></code> defined.  Changes the LLVM ABI.  Also available
by setting <code class="docutils literal"><span class="pre">DISABLE_ASSERTIONS=0|1</span></code> in <code class="docutils literal"><span class="pre">make</span></code>&#8216;s environment.  This
defaults to enabled regardless of the optimization setting, but it slows
things down.</dd>
<dt><code class="docutils literal"><span class="pre">--enable-debug-symbols</span></code></dt>
<dd>Builds LLVM with <code class="docutils literal"><span class="pre">-g</span></code>.  Also available by setting <code class="docutils literal"><span class="pre">DEBUG_SYMBOLS=0|1</span></code> in
<code class="docutils literal"><span class="pre">make</span></code>&#8216;s environment.  This defaults to disabled when optimizing, so you
should turn it back on to let users debug their programs.</dd>
<dt><code class="docutils literal"><span class="pre">--enable-optimized</span></code></dt>
<dd>(For svn checkouts) Builds LLVM with <code class="docutils literal"><span class="pre">-O2</span></code> and, by default, turns off
debug symbols.  Also available by setting <code class="docutils literal"><span class="pre">ENABLE_OPTIMIZED=0|1</span></code> in
<code class="docutils literal"><span class="pre">make</span></code>&#8216;s environment.  This defaults to enabled when not in a
checkout.</dd>
</dl>
</div>
<div class="section" id="c-features">
<h2><a class="toc-backref" href="#id3">C++ Features</a><a class="headerlink" href="#c-features" title="Permalink to this headline">¶</a></h2>
<dl class="docutils">
<dt>RTTI</dt>
<dd>LLVM disables RTTI by default.  Add <code class="docutils literal"><span class="pre">REQUIRES_RTTI=1</span></code> to your environment
while running <code class="docutils literal"><span class="pre">make</span></code> to re-enable it.  This will allow users to build with
RTTI enabled and still inherit from LLVM classes.</dd>
</dl>
</div>
<div class="section" id="shared-library">
<h2><a class="toc-backref" href="#id4">Shared Library</a><a class="headerlink" href="#shared-library" title="Permalink to this headline">¶</a></h2>
<p>Configure with <code class="docutils literal"><span class="pre">--enable-shared</span></code> to build
<code class="docutils literal"><span class="pre">libLLVM-&lt;major&gt;.&lt;minor&gt;.(so|dylib)</span></code> and link the tools against it.  This
saves lots of binary size at the cost of some startup time.</p>
</div>
<div class="section" id="dependencies">
<h2><a class="toc-backref" href="#id5">Dependencies</a><a class="headerlink" href="#dependencies" title="Permalink to this headline">¶</a></h2>
<dl class="docutils">
<dt><code class="docutils literal"><span class="pre">--enable-libffi</span></code></dt>
<dd>Depend on <a class="reference external" href="http://sources.redhat.com/libffi/">libffi</a> to allow the LLVM
interpreter to call external functions.</dd>
</dl>
<p><code class="docutils literal"><span class="pre">--with-oprofile</span></code></p>
<blockquote>
<div>Depend on <a class="reference external" href="http://oprofile.sourceforge.net/doc/devel/index.html">libopagent</a> (&gt;=version 0.9.4)
to let the LLVM JIT tell oprofile about function addresses and line
numbers.</div></blockquote>
</div>
</div>


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